The quantum-splitting phosphor Sr1-xPrxAl12-xMgxO19 where 0<x≦0.2 has been described in U.S. Pat. No. 5,571,451. The quantum-splitting of the Pr3+ ion is of interest because of the potential to produce a phosphor with a quantum efficiency exceeding unity, i.e., producing two visible photons for each UV photon. In the phosphor described above, the insertion of the Pr3+ activator into the lattice for Sr2+ is charge compensated by replacing an equal amount of Al3+ with Mg2+. Because of its quantum-splitting behavior, investigations of this phosphor have been focused on its visible emission at about 400 nm in response to stimulation by vacuum ultraviolet (VUV) radiation at 185 nm.
U.S. Pat. No. 6,613,248 describes alternative compositions designed to increase the amount of visible light emitted from this system. It is therein described that the above-described phosphor also produces a considerable ultraviolet emission in the region from 250 to 350 nm and that this part of the emission reduces the overall visible light output that otherwise might be higher.